Various kinds of square cut or square end gusseted bags have been previously proposed for popping corn in a microwave oven. U.S. Pat. No. 4,691,374 describes a cooking bag in which diagonal gusset seals are provided at the bottom of the bag (FIGS. 1, 3 and 4). Although very good, the bag does have certain shortcomings. Many consumers want a bag that will stand up straight (like a flat-ended paste-bottom bag) when placed on a horizontal surface so that they can easily reach into the bag to take a handful of popcorn. FIG. 9 of the patent has a generally oval shape resembling an inflated football with a fin seal 42 that projects outwardly from the bottom of the bag. While formed from a strip of continuous roll stock which is substantially less expensive than a pasted bottom bag, the bag has at least three shortcomings. First, the bag will not stand upright when placed on a horizontal surface. In addition, the bag will not hold its shape reliably. This causes it to fall over easily if an attempt is made to stand it on end. Third, in the work leading to the present invention, we have now discovered that the tendency of a bag to form an oval or football shape during popping in the oven has a bearing on the ability of the bag to stand up straight as well as on the effectiveness of the susceptor (microwave interactive sheet material) provided in one face of the bag for absorbing microwave energy and transferring the energy in the form of heat to pop the corn.
In view of these shortcomings, it is an important objective of the invention to find a way to help maintain the faces of the bag in a flatter condition than heretofore so as to provide flat, vertically disposed walls when the bag is positioned in an upright position on a horizontal supporting surface such as a table. Another object is to find a way of better controlling the shape of a microwave popcorn bag to give it a more squared appearance that will better retain a rectangular expanded shape as popcorn is being popped within it in a microwave oven.
Another important object is to provide a way of forming a flat-bottomed bag from continuous roll stock material which can be expanded later during cooking so that the bag will stand up reliably when placed on a horizontal supporting surface. Another object is to provide a means of toughening the bag bottom through the addition of a stiffening element to assist the bag in holding its shape. Another object is to prevent the bottom end of the bag from having an oval or football shape following the popping operation in a microwave oven and to provide instead a bottom flat enought to allow the bag to stand up straight when one end is placed on a table or other horizontal surface.
These and other more detailed and specific objects of the present invention will be apparent in view of the following description setting forth by way of example but a few of the various forms of the invention that will be apparent to those skilled in the art once the principles described herein are understood.